The subject matter described and/or illustrated herein relates generally to electromechanical relays, and more particularly, to a pre-charge circuit for an electromechanical relay.
Electromechanical relays are switches that open and close based on an applied electrical current. Different electromechanical relays may be used for different types of applications or based on certain operating parameters. In relatively high voltage applications, electromechanical relays are designed to handle the effects of the relatively high voltage. For example, relatively large capacitors, such as, larger than 500 micro-Farads (g), may be provided to power one or more loads (e.g., in a hybrid electric vehicle (HEV)). The capacitor(s) in this type of application must be pre-charged to avoid a damaging in-rush current being applied to the relay contacts of the electromechanical relay when electrical power is switched on. Essentially, when power is applied to an uncharged capacitor an excessive amount of current rushes to the capacitor. This relatively large in-rush of electrical current may damage the relay contacts of the electromechanical relay. For example, a relatively large in-rush of electrical current may cause the relay contacts of the electromechanical relay to be welded shut. Moreover, a relatively large in-rush of electrical current to the capacitor may cause excessive heating and thereby decrease the life of the capacitor.
In relatively high voltage applications, a pre-charge module may be used to pre-charge the capacitor(s). To pre-charge the capacitor(s), at least some known pre-charge modules include a solid state and/or electromechanical sub-relay in series with a resistor across the relay contacts of the main electromechanical relay that switches electrical power to the capacitor(s). But, pre-charge circuits using solid state and/or electromechanical sub-relays may suffer from reliability issues. For example, the moving switch parts of solid state and/or electromechanical sub-relays may fatigue and thereby ultimately malfunction and/or fail. Moreover, pre-charge circuits using solid state and/or electromechanical sub-relays may be relatively expensive and/or relatively large, which may limit space for other components.